1. Field of the Invention
The invention is related to the production of urea or its equivalent such as ammonium cyanate. More particularly, the invention relates to a catalytic process for the production of these compounds.
2. Description of the Prior Art
Urea or its equivalent, i.e., ammonium cyanate, is used for many economically significant applications. For example, urea is used as a main constituent of fertilizers, as a monomer in the production of plastics, and as an ingredient in animal feed. Large quantities of urea, on the order of 4,000,000 tons/year or more in the United States alone, are synthesized commercially by contacting CO.sub.2 and NH.sub.3 under high pressure, typically 200 to 400 atm., and at temperatures between 140 to 210 degrees C. to form ammonium carbamate, which is then decomposed into urea and water. The high pressures necessitate the use of expensive, sophisticated equipment. Further the low conversion efficiencies usually obtained in this commercial process, e.g., about 50%, require the recycling of unreacted NH.sub.3 and CO.sub.2. Thus, production of smaller quantities by this high-pressure process is not fiscally acceptable. Even if large quantities are desired, the initial capital investment is an obstacle. Since the commercial production of NH.sub.3, a reactant in the process, also involves a high-pressure method which is only economical on a scale of approximately 500,000 tons/year, the monetary and quantity limitations inherent in the commercial urea manufacturing process are further compounded.
Certain situations, however, are most suitable for small-quantity, low-investment techniques. For example, the need for only a relatively small capital investment would facilitate production of urea for fertilizer in a low-technology agrarian country. Similarly, the on-site production of urea from waste by-products of another process is a desirable process usually involving relatively small scales. Such a recovery process is often economically advantageous if a sufficiently high-conversion efficiency from reactant by-products, to salable products is obtainable. These two specific situations and many analogous ones illustrate two important factors. First, techniques involving relatively mild-pressure conditions are important in reducing the associated initial investment and technical complexities. Second, the possibilities of increased efficiency in the utilization of raw materials offered by a high-yield method of making urea from by-products is significant. Thus a relatively mild-pressure, high-efficiency process of making urea is beneficial in many circumstances.